Can individual wave energy converters effectively share power take offs to reduce costs within arrays?

Energy converted from ocean waves has the potential to make a significant contribution to the worlds energy requirements. However to do this wave energy converters will need to form part of wave energy farms, where arrays of devices are deployed in the same geographical vicinity. Current plans for arrays of point absorber wave energy converters generally have devices with individual PTO systems. These generate electricity locally, which is then delivered to a central hub before being transmitted ashore.

In this project an alternative to each device having an individual PTO is investigated, with the aim of significantly reducing the cost of arrays. Several individual point absorber devices will pump air to and from a single central common PTO, which will then generate electricity centrally. Such a configuration has the potential for significant cost savings, resulting from a reduction in the amount of electrical generation technology used within the array. There are also potential power smoothing effects resulting from several point absorbers, at different stages in their power capture cycle, feeding into the same PTO. However by sharing a common PTO control strategies, such as latching and variable damping, can no longer be applied to individual devices. There will also be losses brought about by the longer transmission distances of air between the power capture mechanism and the PTO. This may be significant. The use of a common PTO will also further complicate the intra array effects between individual point absorbers within the array.

The project will examine these potential advantages and disadvantages of using a common PTO, with the aim of providing design guidance to the wave energy industry and research community. The work is being conducted as a collaboration between Plymouth University and Dalian University of Technology. Physical experiments will be conducted at Plymouth University with arrays of up to 4 devices and at two different scales. Results from these measurements will then be used to validate both a frequency and a time domain model developed at Dalian University of Technology. The numerical models can be used to model larger arrays and different configurations, before finally both experimental and numerical results are used to provide design guidance on the use of common PTO.

The research project proposed here will investigate the use of a common PTO within arrays of point absorber wave energy converters. Instead of individual devices each having a turbine and generator several devices within an array pump air through a common PTO. It is anticipated that this concept could provide significant savings in the cost of arrays of devices, as well as potential smoothing effects in the flow delivered to turbines.

There is clearly a long term benefit in research development that leads to improvements and cost reductions in the wave energy industry. The benefit is to society at large in contributing to the development of the wave energy industry, providing a renewable source of energy, reducing carbon emissions, proving greater energy security for the UK and China, in an environmentally sensitive manner.

Research developments made in this project will add to both UK and China expertise in the new wave energy industry, with the potential to develop into a significant export industry for both countries. Research training in the field of wave energy and wave tank testing for the PDRA will benefit the industry and academic community. The establishing of collaborative links between the research communities at Plymouth University and Dalian University of Technology will be of benefit to the industry in both countries, with the potential for collaborations in marine renewable energy envisioned.

The results of this research will be disseminated through the usual channels by presentations at international conferences such as EWTEC, AWTEC and the Marine Energy Conference of China, at national professional body conferences and special interest groups, such as ICE and RINA and by publication in peer reviewed journals. In addition the project findings will be disseminated to the academic and industry communities through the PRIMaRE network and through the principal investigators links to SuperGen UKCMER on other projects.

In order to make the impact happen, we propose to carry out the following activities:
1. Involve key stakeholders, academics and key industrialists through the PRIMaRE network collaboration and the South West Marine Energy Park.
2. Create a website to guide interested parties to the information produced.
3. Disseminate results within China via the Marine Energy Conference of China.